There are already known to exist respiratory assistance devices comprising means to bring the respiratory gas into the lungs of a patient, and to possibly remove said gas from these lungs, by means of a respiratory assistance tube whose distal extremity is generally intended to be introduced into the windpipe of the patient. In this case, it is normal practice to dispose an inflatable ballonet at the distal extremity of the probe. Accordingly, there is a risk of excess pressure occuring in the lungs of the patient if feeding of the gas is not strictly controlled, this excess pressure frequently proving to be dangerous for the patient.